With the evolution of more complex infrastructures requiring enhancement, replacement, and expansion in all areas of human occupation, and in particular high-density areas such as cities and suburbs, the ability to accurately map the location of buried conduits, wires, and pipelines of various sizes and kinds becomes more pressing, as does the need to document actual as-built underground installations before they are covered so that they can be precisely located at a later date.
Worker safety and project economic concerns also require the location and identification of existing underground utilities such as underground power lines, gas lines, phone lines, fiber optic cable conduits, cable television (CATV) cables, sprinkler control wiring, water pipes, sewer pipes, etc., collectively and individually herein referred to as “buried objects.” As used herein, the term “buried objects” includes objects located inside walls, between floors in multi-story buildings or cast into concrete slabs, for example, as well as objects disposed below the surface of the ground.
The unintended destruction of power and data cables may seriously disrupt the comfort and convenience of residents and bring huge financial costs to businesses. Therefore human-portable locators have been developed that sense electromagnetic emitted signals to thereby locate buried utilities such as pipes and cables. If the buried conductors carry their own electrical signal, they can be traced by detecting the emitted signals at their appropriate frequency. Signals with a known frequency are also applied to pipes and cables via a transmitter to enhance the ease and accuracy of the line tracing.
Portable utility locators or buried object locators typically carry one or more antennas that are used to detect the electromagnetic signals, and typically magnetic field signals, emitted by buried pipes and cables, as well as sondes that have been inserted into pipes. The accuracy of portable utility locators is limited by the sensitivity and the configuration of their antennas. Moreover, precise locating of the position of a locator on the surface of the earth—as would be needed, for example, in order to build an accurate digital map of the locating results—has been problematic because of imprecise positioning technology and an inability to track the position of a locator relative to the ground itself.